Longevity Briefs: Reversing Hearing Loss By Restoring Damaged Cells In The Ear

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Longevity briefs provides a short summary of novel research in biology, medicine, or biotechnology that caught the attention of our researchers in Oxford, due to its potential to improve our health, wellbeing, and longevity.

Why is this research important: Hearing loss is a common occurrence during ageing, beginning with a reduced ability to hear higher frequencies, with hearing loss spreading down the frequency range with advancing age. This happens in part because of the death of special cells called hair cells within the snail shell-like cochlea of the ear. These cells are responsible for converting sound waves into electrical signals that encode the amplitude of the sound, while their location within the cochlea encodes the pitch (frequency). Lower frequency sound waves travel further into the cochlea, and we lose the ability to hear high frequency sounds first because we lose the hair cells closer to the ear drum first.

Above: scientists have been able to isolate a single hair cell and watch it ‘dance’ to music.

Anyone who has experienced having their ears blocked can confirm that impaired hearing is surprisingly debilitating, and can lead to feelings of isolation. Hearing loss is also correlated with dementia. Hearing aids are the most common solution for hearing loss, but what if we could restore hearing by regrowing the hair cells that have been destroyed?

What did the researchers do: A biotechnology company called Frequency Therapeutics is exploring a new kind of regenerative therapy for hearing loss. It uses small molecules injected directly into the ear in order to program progenitor cells, the descendant of stem cells in the inner ear, to generate new hair cells. Progenitor cells generate hair cells in the developing foetus, but become dormant before birth. The company has already conducted multiple clinical trials including over 200 participants in total. The number one goal of these trials was to see if the therapy can improve speech perception – the ability to understand speech and recognize words.

These are images of cross-sections of the cochleae of mice that had hearing loss, taken 30 days after receiving either a control (left) or Frequency Therapeutics’ treatment (right). Hair cells are labelled with a pink stain, while DNA is stained blue. You can see that in the image on the left, few hair cells remain in the region closest to the eardrum (within the dotted line), while the hair cells of the treated mouse have been largely restored.
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Key takeaway(s) from this research: So far, three out of four separate clinical trials have found the treatment to be more effective than placebo in improving speech perception, with some participants needing only a single injection to experience meaningful improvements lasting up to two years. A phase 2 clinical trial with 124 participants is currently recruiting and should have results next year.

The nice thing about this approach to regenerative medicine is that it works by targeting progenitor cells that already exist within the patient’s tissues, rather than requiring the patient’s cells to be extracted, reprogrammed and reintroduced into the target tissue. This would make it a much more straightforward and less labour-intensive type of treatment that could be applied to other tissues throughout the body that contain progenitor cells (we recently reported a regenerative therapy targeting progenitor cells in the heart).